How the most important plant for Prehistoric Man migrated across the planet

The bottle gourd, otherwise known as the calabash plant, was prehistoric man’s most useful plant. It is believed to be the first cultivated plant in the world, and may have been domesticated even earlier than food crops and livestock.  Its’ hard-skinned fruit was used to make water bottles, spoons, pipes, containers, musical instruments, and ornaments. They were also used to make pontoons in ancient Egypt, swimming aids by the Romans, birdhouses by Native Americans, and more recently as motorcycle helmets in Nigeria. It is the only known plant whose use by humans spanned prehistoric cultures across the entire globe, but one thing that has puzzled scientists was how – given its African origins – it came to be so widely used in Asia and the Americas at least 8,000 – 10,000 years ago.

The prevailing assumption was that the Calabash spread across oceans, from Africa to America, without human intervention, if the seeds were still able to germinate after long periods at sea.  However, a genetic study in 2005, led by botanist David Erickson of the Smithsonian Institution, overruled this theory and concluded that the American strain of the plant originated in Asia, so were most likely carried across the Beringian land-bridge from Siberia to Alaska by Paleo-Indian migrants around 16,000 years ago.  However, there is little supporting evidence that the bottle gourd was ever used in Siberia or Alaska in the late Pleistocene era (they tended to use animal hides for storage rather than plants).  Most importantly, how could the bottle gourd, a tropical plant, make it through years of traveling across the Arctic?

A new, more advanced, study of the bottle gourd’s DNA, led by molecular anthropologist Logan Kistler of Pennsylvania State University, has overturned Erickson’s theory and concluded that the initial hypothesis was correct – the gourd’s seeds drifted across the Atlantic Ocean from Africa to the Americas, then took root and grew wild in the New World.  Much later, Paleo-Indians arrived and started to domesticate them from around 10,000 years ago.

Kistler’s team analysed 86,000 base pairs of ancient and modern bottle gourds’ chloroplast DNA, which can be used to build family trees for plants. The genetic analysis revealed that pre-Columbian bottle gourds in the Americas were more closely related to African gourds than those found in Asia. Using updated models of how objects drift on Atlantic currents, Kistler’s team concludes that the ancestors of New World bottle gourds probably floated to the West African coast by river and landed on the coast of Brazil an average of 9 months later.

While the study authors are confident in their conclusions and assert that “now, it’s really quite clear that [the bottle gourd] reached the New World under its own steam,” not all the questions about the bottle gourd have been answered. Scientists don’t know how it got to Asia, for example, and the scarcity of wild bottle gourds the world over begs the question of why uncultivated varieties of the plant disappeared.  For now, these pieces of the bottle gourd’s past remain mysterious.

By April Holloway